(1) Field of the Invention
The present invention relates to a high-pressure discharge lamp and an arc tube built in the high-pressure discharge lamp.
(2) Related Art
As an example of conventional high-pressure discharge lamps, there is a known metal halide lamp that is disclosed in the Japanese Laid-Open Patent Application No. H06-196131.
This metal halide lamp includes an arc tube having a main tube part and a pair of capillary tube parts. The main tube part has a pair of electrodes arranged opposite to each other in an internal discharge space. The pair of capillary tube parts is disposed at both ends of the main tube part and continues into the discharge space. In each of the capillary tube parts, there arranged a rod-like feeder for providing a current the corresponding electrode carries from outside. The feeder is sealed to the capillary tube part with a seal member such as frit glass.
The feeder consists of two different types of metal which are connected into a rod. That is to say, a metal with high halogen resistance, such as tungsten, is used in one part of the feeder extending from the inner electrode to the middle of a capillary tube part, and niobium, whose thermal expansion coefficient is closer to that of the seal member, is used for the other part of the feeder extending from the middle to outside. Only the niobium portion of the feeder is sealed with the seal member.
According to the above application, having such a sealing structure prevents corrosion of the part of the feeder which is exposed to halides the discharge space, since that part of the feeder is made of tungsten which is highly resistant to halides. Also, no crack will be produced due to thermal stress, since the feeder is sealed with the seal member at the niobium portion and niobium has a thermal expansion coefficient approximate to those of the seal member and the capillary tube part. This extends the lamp life substantially.
However, it was found in the actual fact that a leak of halides can occur in the sealed area even with the stated construction, which makes it impossible to ensure a sufficient lamp life.
Which is to say, though the niobium portion of the feeder arranged in the capillary tube part is covered with the seal member, as the temperature inside the capillary tube part rises to as high as several hundreds of degrees in the centigrade scale, the reaction between the metal halides and frit glass which is used as the seal member tends to occur, making the frit glass degenerated and weaker. As a result, every time the light is turned on and off, micro cracks are formed in the frit glass, in an area extending from the end of the seal member on the side of the discharge space to the other end of the feeder.
The occurrence of such cracks does not cause a leakage of the metal halides. However, since niobium is easily corroded by halides, corrosion can advance at a brush, once the halides that are penetrating into those micro cracks reach the surface of the niobium. This results in the occurrence of a space in places where niobium contacts with the seal member, causing a leak of metal halides enclosed inside the seal member, thereby rapidly decreasing luminous efficacy of the lamp.
Another metal halide lamp is devised that uses as a feeder only a conductive cermet, which is a sintered mixture of tungsten and alumina, instead of using two types of metals of different properties as described above.
However, this material is of low mechanical strength, and a portion of the conductive cermet that is protruding from a capillary tube part is easily broken by external impact and vibration.
A typical metal halide lamp is constructed in which a part of each feeder, which is protruding from an end of an arc tube, is connected to a feeding stem wire fixed to a base, so as to hold the arc tube to the base by means of the feeding stem wires. Therefore, if the protruding part is broken by external impact, the metal halide lamp becomes unusable.
High-pressure discharge lamps other than metal halide lamps also contain some kinds of halides to extend a lamp life by using halogen cycle. Therefore, the above problem can occur in these high-pressure discharge lamps, too.
In view of the above problems, it is an object of the present invention to provide a high-pressure discharge lamp that is not easily broken by external impact or vibration and can operate longer hours of time, by preventing halides from corroding into a feeder. Another object of the present invention is to provide an arc tube built in the high-pressure discharge lamp.
To achieve the first object, a high-pressure discharge lamp having an arc tube is provided. The arc tube includes an arc vessel having a main tube part and a pair of capillary tube parts, the main tube part having an inner discharge space, the capillary tube parts continuing into the discharge space; a pair of electrodes being opposed to each other in the discharge space: a pair of feeders, each of which is inserted through a different one of the capillary tube parts with an end connected to one of the electrodes on a side of the feeder and a remaining end protruding from the capillary tube part to outside; and a seal member for sealing the feeders in the capillary tube parts, wherein at least one of the feeders includes a first conductive member being sealed in the capillary tube part and a second conductive member being connected to the first conductive member outside the capillary tube part, the first conductive member being resistant to halides, the second conductive member being fixed with a fixing member at an end of the capillary tube part.
With the stated construction, a portion of the first conductive member of at least one of the feeders that is located inside the capillary tube part is halogen-resistant, which reduces the possibility of the feeder being corroded by halides that have penetrated in the seal member during the lighting. This prevents an enclosed substance from being leaked to outside. Also, the feeder has a second conductive member located outside the capillary tube part, which is different from the first conductive member. With the use of a material that has a great mechanical strength or is flexible, and with the second conductive member being fixed with a fixing member, it is possible to prevent a breakage of the feeder on external impact or vibration, thereby extending the lamp life.
The fixing member which is the seal member. With the stated construction, the sealing member used to seal the capillary tube part can also be used to fix the second conductive member to the capillary tube part, thus streamlining the manufacturing processing.
The high-pressure discharge lamp is provided with the fixing member so as to at least partially cover a connecting portion where the first conductive member is connected with the second conductive member. With the stated construction, it is possible to fix the second conductive member to the capillary tube part while increasing the mechanical strength of the connecting portion where the first conductive member is connected with the second conductive member.
The high-pressure discharge lamp is provided with the fixing member so as to completely cover a connecting portion where the first conductive member is connected with the second conductive member. With the stated construction, the mechanical strength of the connecting portion is further increased.
Note that the expression xe2x80x98the connecting portion where the first conductive member and the second conductive member is connectedxe2x80x99 refers not only to a portion where they are connected mechanically in actual terms by laser welding or resistance welding, but also a portion where the first conductive member contacts to the second conductive member.
The high-pressure discharge lamp is provided with a connecting portion where the first conductive member is connected to the second conductive member in a vicinity of the end of the capillary tube part. With the stated construction, the second conductive member is located close to the capillary tube part, thereby reducing the amount of the fixing member required to fix the second conductive member to the capillary tube part.
The high-pressure discharge lamp is provided with the first conductive member and the second conductive member connected so that ends of the first conductive member and the second conductive member are placed side by side. With the stated construction, the size of a contact area where the first conductive member electrically contacts to the second conductive member is increased, and the welding of the first and the second conductive members into such a rod-like shape is easier than welding them into a straight rod.
The high-pressure discharge lamp is provided with an end surface of the second conductive member facing the first conductive member substantially so as to contact an end surface of the capillary tube part, and an inner diameter D(mm) of the capillary tube part, an outer diameter d1 (mm) of the first conductive member, and an outer diameter d2 (mm) of the second conductive member satisfy, d1+d2 greater than D . With the stated construction, the second conductive member can be used as a stopper, making it easier to determine the location of the electrodes in the main tube part during the manufacture.
The high-pressure discharge lamp is provided so that at least an end of the second conductive member facing the first conductive member has a cylindrical shape, and the first conductive member is inserted into the cylindrical part of the second conductive member to be connected to the second conductive member. With the stated construction, the mechanical strength of the connecting portion where the first conductive member is connected to the second conductive member is increased, and a breakage of the feeder due to external impact or vibration can be prevented with considerable effectiveness. Also, a contact area where the first conductive member contacts to the second conductive member is increased in size, so that electrical connection between the two members is ensured.
The high-pressure discharge lamp is provided so that a cylindrical end surface of the second conductive member facing the first conductive member is provided substantially in contact with an end surface of the capillary tube part, and an inner diameter D(mm) of the capillary tube part and an outer diameter d3 (mm) of the cylindrical portion satisfy, d3 greater than D. With the stated construction, the second conductive member can be used as a stopper, serving to determine the location of the electrode in the main tube part during the manufacture.
The high-pressure discharge lamp is provided so that a cylindrical end surface of the second conductive member facing the first conductive member is provided substantially in contact with an end surface of the capillary tube part, and an incision part is provided at an end of the cylindrical part of the second conductive member, the incision part allowing for a connection between an inner space and outside, the inner space being situated between the capillary tube part and the first conductive member. With the stated construction, a melted seal member can flow through the incision part into a space between the capillary tube part and the first conductive member, ensuring the sealing processing.
The high-pressure discharge lamp is provided so that a cylindrical end surface of the second conductive member facing the first conductive member is provided substantially in contact with an end surface of the capillary tube part, and an incision part is provided at an end of the capillary tube part, the incision part allowing for a connection between an inner space and outside, the inner space being situated between the capillary tube part and the first conductive member. With the stated construction, the same effects can be achieved as in the case where the incision part is provided in the first conductive member.
The high-pressure discharge lamp includes a fringe at a cylindrical end of the second conductive member facing the first conductive member, the fringe being placed substantially in contact with an end surface of the capillary tube part. With the stated construction, the feeder is securely supported by the fringe and can withstand to impact on the second conductive member perpendicular to the longitudinal direction of the second conductive member. This further reduces the possibility of the feeder being broken off.
The fringe has a thickness of 0.2 mm to 1.0 mm. With the stated construction, the fringe is strong enough to be used for a backup use, which further reduces the possibility of the feeder being broken off.
The high-pressure discharge lamp includes a taper at the cylindrical end of the second conductive member facing the first conductive member, the taper flaring towards the first conductive member, an end of the taper substantially contacts to an end surface of the capillary tube part. With the stated construction, the feeder is firmly supported by the taper and can withstand to impact on second conductive member in a direction perpendicular to the longitudinal direction of the second conductive member. This further reduces the possibility of the feeder being broken off.
The high-pressure discharge lamp includes a ringed member through which the second conductive member is inserted, wherein the ringed member is provided substantially in contact with the end surface of the capillary tube part and fixed to the second conductive member and an end surface of the capillary tube part with the fixing member. With the stated construction, the ringed member is attached to the second conductive member to fix the feeder to the capillary tube part firmly. This further reduces the possibility of the second conductive member being broken off.
The high-pressure discharge lamp is provided wherein the so that the first conductive member is connected to the second conductive member so that the first conductive member is arranged perpendicular to the second conductive member longitudinally. With the stated construction, the high-pressure lamp becomes shorter in length than in the case where the ends of the first conductive member and the second conductive member are placed in parallel.
The high-pressure discharge lamp is provided so that a difference in a thermal expansion coefficient between the first conductive member and the seal member is equal to or smaller than a difference in the thermal expansion coefficient between tungsten and the seal member. With the stated construction, there is a reduction in the level of thermal stress generated during the lamp operation between the first conductive member and the seal member due to a difference in thermal expansion coefficient. As a result, the possibility of the occurrence of a crack in the seal member is further reduced.
It is preferable that the first conductive member is made of a conductive cermet. Since the conductive cermet has a thermal expansion coefficient approximate to that of frit glass which is used commonly as a seal member, the conductive cermet can more effectively prevent the occurrence of a crack produced by thermal stress.
The high-pressure discharge lamp is provided so that the second conductive member is chiefly made of niobium. Niobium has a greater mechanical strength than the first conductive member, which is generally resistant to halides, and has a thermal expansion coefficient closer to that of the seal member. The use of the seal member as a fixing member therefore does not lead to the occurrence of a crack at a supporting point of the sealed area, increasing the mechanical strength of the arc tube considerably.
To achieve the second object of the present invention, the arc tube related to the present invention has an arc tube including an arc vessel including a main tube part and a pair of capillary tube parts, the main tube part having an inner discharge space, the capillary tube parts continuing into the discharge space; a pair of electrodes being opposed to each other in the discharge space: a pair of feeders, each of which is inserted through a different one of the capillary tube parts with an end connected to one of the electrodes on a side of the feeder and a remaining end protruding from the capillary tube part to outside; and a seal member for sealing the feeders in the capillary tube parts, wherein at least one of the feeders includes a first conductive member being sealed in the capillary tube part and a second conductive member being connected to the first conductive member outside the capillary tube part, the first conductive member being resistant to halides, the second conductive member being fixed with a fixing member at an end of the capillary tube part. With the stated construction, a portion of the first conductive member of at least one of the feeders that is located inside the capillary tube part is halogen-resistant, which reduces the possibility of the feeder being corroded by halides that have penetrated in the seal member during the lighting. This prevents an enclosed substance from being leaked to outside. Also, the feeder includes a second conductive member located outside the capillary tube, which is different from the first conductive member. With the use of a material that has a greater mechanical strength or flexibility, and by fixing the second conductive member to the capillary tube part by means of a suitable fixing member, the breakage of the feeder on external impact or impact can be prevented, and thus an arc tube having a longer operating lifetime can be obtained.